The invention relates to an alignment device for indicating alignment between two component parts and, more particularly, to a level indicator comprising such an alignment device which is particularly suitable for use in a power tool.
It is well known that a pivotally mounted and weighed body will seek an equilibrium position under the influence of gravity. A particular and specific digital angle indicator device utilising this principle is disclosed in U.S. Pat. No. 4,253,242 which shows an axially mounted and weighted disk, rotatably mounted relative to a fixed body. The weighted portion of the disk is responsive to gravity and rotates relative to the body. The body comprises an indicator surface used to align the body to a horizontal plane in such a position the disk will have aligned itself relative to the body so that apertures in the disk will allow the transmission of light from a light source to a light detector through one of a plurality of holes in the disk, detection of the light source indicating the alignment and thus the obtaining of a horizontal or predetermined angular plane. However, a device of this type requires very accurate manufacturing techniques and the use of jewel bearings to allow appropriate and free rotation of the disk within the body. In addition, since the rotatable disk utilises a balance weight in order to be responsive to gravity, such a weight provides a moment on the bearing which can be emphasised to a detrimental affect is any additional and undue force is created such as by dropping the device. This undue force could be transmitted directly through the disk to the axial bearings which could damage the bearings and alignment of the device. These drawbacks are particularly relevant to use of such a device in a robust environment.
This type of alignment device has potential uses in obtaining angle or level measurements. In many activities it is desirable to obtain a level reading, particularly within the construction industry or general DIY activities such as hanging doors or putting up shelves. The conventional method of obtaining a level is the use of a conventional spirit level utilising a simplistic arrangement of a straight sealed tube filled with a liquid and having a small bubble or air gap left in the liquid. The tube is marked with two lines whereby when the tube (usually in a flat mounting board) is laid horizontally the bubble within the tube will align between the two lines in the centre of the tube to indicate that the tube and carrier are perfectly horizontal.
An alternative method of measuring the horizontal is to utilise a simplistic pendulum having a rigid straight bar connecting the pivot point with a hanging weight together with a crossbar mounted at 90xc2x0 to the vertical bar. The crossbar can be disposed either side of the pivot point whereby when the pivot level is hung and the weight achieves equilibrium the crossbar will be positioned in a horizontal plane and then its ends may be aligned with two notches on a carrier board to align the board to the horizontal and thus measure the horizontal. These are simplistic mechanical devices for measuring the horizontal level.
However, the drawbacks of conventional levels of this type are their sensitivity and unwieldy size making it difficult to use in certain applications. In particular, the use of a power drill requires a preferential alignment of the tool axis horizontally or vertically to allow a hole to be bored in at 90xc2x0 to an upright material or horizontal material respectively. Obviously, the use of a conventional spirit level in a drill has significant drawbacks whilst when aligning a drill to the horizontal it will be effective to indicate when the drill is level (in the same manner as a conventional spirit level) but once the drill is activated, the vibrations caused by the power tool will be transmitted to the liquid medium in the spirit level which will then xe2x80x9cfrothxe2x80x9d due to the vigorous vibrations. Thus, the spirit level is subsequently rendered useless. Furthermore, a liquid spirit level cannot determine a vertical plane directly. Alternatively, the use of a pendulum type level indicator of the type described above in a drill is feasible but due to its sensitivity and lack of damping together with the associated unwieldy size such a product would not be convenient for use in a drill.
It is therefore an object of the present invention to provide an alignment device which is simplistic and cost-effective to manufacture and alleviates the aforementioned problems.
It is a further object of the present invention to provide a level indicator incorporating such an alignment device and also to provide a power tool incorporating such a level indicator.
According to the present invention there is provided an alignment device for indicating alignment between two component parts, wherein a first component part comprises a main body having a concave track and a track following member restrained in engagement with and displaceable about said track to follow said track under the influence of gravity to seek an equilibrium position; a second component part comprises an alignment member pivotally mounted within said body and restrained in engagement with said track following member so as to be directly pivotally displaceable in response to displacement of said track following member, said device further comprising a first alignment port and a second alignment port in said body and indicator means for providing an indication when said alignment member is in a predetermined alignment with both first and second alignment ports.
According to another aspect of the present invention there is provided a level indicator comprising this alignment device. Preferably such level indicators using this alignment device are used in power tools, particularly power drills.
There is further provided an invention relating to an electrical trigger switch for a power tool comprising a trigger having first and second elongate switching members longitudinally displaceable against a resilient biasing force into engagement with first and second electrical switching elements respectively, whereby longitudinal displacement of said trigger moves said first switching member into engagement with said first switching element to effect a first switching operation and continued longitudinal displacement of said trigger moves said second switching member into engagement with said second switching element to effect a second independent switching operation.